In many video coding systems, pictures that have been decoded earlier can be used for prediction of the image data of later pictures so that only the difference needs to be encoded. As known in the art, this prediction greatly reduces the size of the coded data. To be able to perform prediction, the earlier decoded pictures need to be stored, often temporarily, to the memory so that they can be quickly retrieved for prediction. When more and more pictures are decoded, older reference pictures need to be dropped away from the memory to e.g. make space for new ones. That is, some new pictures that have been decoded are marked to indicate that they are to be used for reference, and kept in the reference picture memory. Some decoded pictures are marked unused for reference and they can be dropped from the memory. To carry out this process effectively, the pictures to be used for reference can be signaled in the video transmission. However, additional signaling in the video transmission adds to the amount of data that needs to be sent.
There is, therefore, a need for solutions that improve the reference picture handling process without undermining coding efficiency.